Re: Smaller Speakers/tube amps, blah, blah, blah.....

At 4:19 AM -0600 3/14/98, John Pollock wrote:
>Sean T Barrett wrote the stuff with >, and Kim's quotes get > >:
>>
>> kim:
>> >I guess you're not a guitar player, right? An electric guitar
>> >by itself is only half the instrument.
>> [snip]
>> >That is also why a guitar through a flat PA system will sound
>> >very bad, and to the player, it will feel lifeless.
>
>That _can_ be the case, but isn't necessarily always true. It depends
>on the guitar's pickups, the impedance loading them, the strings, and
>the musical context.
>
>Most electric guitars have passive magnetic pickups. If they're loaded
>too heavily (i.e., the input impedance of the amplifier is too low), the
>high frequencies will be rolled off severely. The hi-Z inputs of most
>PA systems, typically 50K, will of course strangle the signal from most
>passive magnetic pickups. (The typical guitar amp's 220K is actually a
>bit low as well, but in this case it's a _feature_, slightly rolling off
>the upper harmonics so they don't clash quite so badly with the
>harmonics the amp has been carefully designed to generate.)
probably the last I have to say about this, since it's getting off
topic....
Another effect of the guitar/tube amp thing, and what I meant by the "amp
is half the instrument" comment, is that the input impedance of a tube
amplifier is not a constant thing. It changes as the current in the tube
changes. This means that the impedance will change a bit depending on the
signal. Guitar pickups are high output impedance devices, so the impedance
of the input stage of an amplifier will have a strong affect on the
pickup's frequency response. So this means, as you pick a note, the tube
amp input will actually change the frequency response of your pickup over
the course of the note. I think most of this effect will occur during the
attack since you would have a large current change then, and that's where
most people hear it.
For any other amplifier application, this is a serious flaw. But for
guitars it's a bit different. In that case, this strange affect becomes
something you use as a means of controlling timbre in your sound, therefore
making it part of the "instrument". I don't think most people are real
conscious of what is going on, they just know that a big variation in sound
happens depending on how they pick. It becomes an intuitive part of how you
play. (Tube amp player's often refer to this as "bounce".) If you then play
into a solid state input (by putting some pedals between guitar and amp,
using active pickups, or using a solid state amp), you notice that the
sound is less responsive. It seems lifeless. This is because the input
impedance is very stable, and that frequency respnse jiggle in the pickups
is gone. (similar things happen between the output of a tube amp and the
speakers.)
This doesn't have much to do with the character of the sound itself. It's
really about how the guitar/amp combination feels to the player. And that
of course, can inspire the player in creative ways. It also leads to people
obsessing about amplifiers and they're signal chain.
And as far as the response of "I've done it this way for years, and it
sounds fine to me", well, I been there! I had pedals and solid state guitar
amps for the first 18 years of playing I did. And then I took that tube amp
drug, and before long I was totally hooked. Once that bounce has gotten
worked into your playing, and you learn to control that aspect of the
sound, you'll be heading down to the corner tube pusher on a regular basis,
mainlining EL-84's, doing 12AX7/6L6 speedballs....
kim
______________________________________________________________________
Kim Flint | Looper's Delight
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